The long-term objective of this project is to characterize the cognitive and linguistic mechanisms that underly the spelling (writing) process and the ways in which this process may be disrupted as a consequence of brain damage. The specific aims of the project are: 1) to evaluate the hypothesis that specific forms of spelling dysfunction (dysgraphia) result from damage to distinct components of the spelling process; and 2.) to characterize in detail the internal structure of the components assumed to comprise the spelling system, thereby providing a basis for a deeper understanding of the various forms of spelling disorders found in brain-damaged patients. These aims will be accomplished through a two-phase program of research. In the first phase, a large number of patients with focal brain damage will be tested with a spelling test battery, specially designed to distinguish among various types of spelling disorders. Patients' performance on the test battery will be used to a) evaluate models of the spelling process and b) define subgroups of patients with selective deficits to various components of the spelling process. In the second phase, patients with selective deficit to particular processing components (e.g., the component that stores knowledge of the orthographic structure of words) will be tested with sets of experimental tasks designed to probe in considerable detail the strucure of the various components involved in spelling. Information generated from the detailed analyses in this phase of the project will be used to a) revise the test battery to better discriminate among different types of spelling disorders and b) evaluate specific hypothesis about the internal structure of particular components of processing. A further major component of the proposed research involves the use of computational modelling techniques. This aspect of the proposed research will allow the formulation of a computationally-explicit model of the spelling process and the stimulation of spelling disorders by the "experimental lesioning" of the implemented model. Finally, the detailed characterization of spelling disorders in terms of damage to specific components of the cognitive/linguistic mechanisms that underly spelling will be used to explore correlations between locus of brain damage and type of functional disorder. The results of the proposed studies will contribute to a deeper understanding of the basis for spelling disorders in brain-damaged patients--an indispensable foundation for the diagnosis and remediation of dysgraphia.